Sparking plug for internal combustion engines



Aug. 11,1942.

c. J. ,SMITHELLS SPARRING PLUG FOR INTERNAL COMBUSTION ENGINES Filed May 27, 1941 Patented Aug. 11, 1942 UNITED STATES PATENT OFFICE SPARKING PLUG FOR. INTERNAL COMBUSTION ENGINES Colin James Smithells, Rugby, England, assignor to Lodge Plugs Limited, Rugby, England Application May27, 1941, Serial No. 395,477

1 Claim.

This invention relates to sparking plugs for internal combustion engines. It is desirable in such a, plug to effect between the earthed electrode (or each such electrode) and the body, a connection of good thermal conductivity in order that when the plug is in use heat may be con- In Great Britain June 22, 1940 ducted rapidly from the electrode to the body the said electrode is electrically welded to the body under pressure by fusion of the body only.

In the accompanying sheet of explanatory drawings:

Figure l is a part sectional elevation, and Fig.- ure 2 aninverted plan, of a sparking plug embodying the invention.

Figure 3 is a fragmentary sectional elevation illustrating a modification of the invention.

In the drawing the bodypf the plug is indicated by a, the earthed electrodes by b, and the central or insulated electrode by c. As shown a pair of earthed electrodes b are provided and are-arranged so that their free ends lie at opposite sides of the central electrode 0, but it is to be understood that only one earthed electrode may be provided if desired. y

In carrying the invention into efiect as shown the body a is made from mild steel, and the earthed electrode or each of the earthed elecsuch electrode b is electrically welded either toa shoulder dformed on the interior of the body a at a position adjacent to its inner end as shown in Figures 1 and 2, or to the inner end of the body as shown in. Figure 3. In connecting the earthed electrode or each earthed electrode b to the body a, the latter is gripped by a copper electrode as close as possible to the point at which the connection is required, and. another copper electrode is arranged to press on the adjacent end of the wire forming the earthed electrode under. a pressure of about 20 pounds. The welding current is supplied from a transformer giving a secondary voltage of about 12 volts. The steel body it melts at the point of contact with the wire and the latter sinks into it under the applied pressure, the steel displaced by the Wire being indicated by e in the drawing. The wire is not deformed by this process but is pressed sufliciently into the body to effect the required connection of good thermal conductivity between the wire and body. It will be seen therefore that the earthed electrode or each such electrode is electrically welded to the body under pressure by fusion of the body only.

The invention is not limited to the example above described as subordinate details as regards the composition of the body and earthed trodes b is made froma convenient short length of wire of about .025! square cross section, the wire being made from a platinum-iridium alloy which has a composition of approximately electrode or electrodes, the shape and dimensions of either of the parts, or the mode of effecting the electrical welding of the parts together under pressure may be varied to suit different requirements.

Having thus described my invention what I claim as new and desire to secure by- Letters Patent is:

A sparking plug having in combination with a.

hollow metal body, at least one earthed electrode which is made from metal having a considerably higher melting point than that of the body, and

v which is welded to and partly embedded in the body, the .latter having projecting from its inner peripheral surface metal displaced by the embedded part of the electrode. I

COLIN JAMES SMITHELLS. 

